involution

...In permafrost zones, the landforms that develop include ice wedges, which are water that fills cracks and freezes, giant polygons with diameters of tens of meters, palsas, which are mounds of peat with a thin layer of ice and diameters of several meters to several tens of meters and heights of several meters, pingos, which are even larger mounds with ice blocks inside, ice masses that accumulate under the ground surface, and shallow basins and thawing lakes that form when ice melts. In the cross section of the permafrost phenomenon, complexly distorted folding and intrusion structures called involutions and thaw mixing phenomena such as the rise of gravel with its long axis oriented vertically in the soil can be seen. The freeze-thawing process erodes the mounds of bedrock and develops unique slope shapes. ...

*Some terminology explanations that mention "involution" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…永久凍土地帯では，凍結割れ目を満たす水が凍った氷楔（ひようせつ）ice wedge，それが作る径数十mの巨大多角形土polygons，氷の薄層をもつ径数m～数十m，高さ数mの泥炭の高まりであるパルサpalsa，さらに大型で中に氷塊をもつ小丘ピンゴpingo，地表下に集積した集塊氷，それが溶けてできた浅い盆地アラスalasや融解湖などの地形が発達する。凍土現象の断面には，インボリューションinvolutionという複雑にゆがんだ，褶曲･貫入構造や，土中の礫が長軸を垂直方向に向けた礫の立ち上がりなどの，融凍攪拌現象がみられる。凍結削剝作用は，基盤岩の高まりを削って，特有の斜面形を発達させる。…

※「involution」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報